The present invention generally pertains to the field of optical switching and fiber optics, and relates to optical switching devices and fiber optic components. More particularly, the present invention relates to methods for ensuring path integrity in fiber optic switch arrays.
An optical switching device couples light beams from an input fiber to a selected output fiber. With reference to FIG. 1, one such optical switching device 210 includes an input receptacle 212 for receiving a plurality of input fibers 214, a first lens array 216, a first array of mirrors 218 comprising a plurality of mirrors 220 disposed in a first mirror plane 222, a second array of mirrors 224 comprising a plurality of mirrors 226 disposed in a second mirror plane 228, a second lens array 230, and a output receptacle 232 for receiving a plurality of output fibers 234. Mirrors 220 and 226 are placed and controlled in pairs so that light from a given incoming fiber can be directed toward any one outgoing fiber. An optical connection (i.e., completed signal path) is made when a mirror in first mirror plane 222, illuminated by an input fiber 214, directs light toward a mirror in second mirror plane 228, which directs this light toward a selected output fiber 234.
For example, one such signal path is illustrated by a path 236 shown in the Figure. Light output from an input fiber 238 passes through a lens 240 in first lens array 216 and is directed towards a mirror 242 in first mirror plane 222, whereupon it is reflected toward a mirror 244 in second mirror plane 228, which is positioned so as to direct the reflected light toward a lens 246 in second lens array 230, which in turn directs the light toward an output fiber 248.
Signal path 236 illustrates a desired connection path. However, due to various system anomalies, the position of either or both of mirrors 242 or 244 may move, as well as the alignment of other system components, thereby causing a system misalignment, creating a misconnected path, such as a path 250 depicted in the Figure, wherein light received from input fiber 238 is directed toward an output fiber 252 instead of the desired output fiber 248.
It is desired to avoid such misconnected paths. It is also desired to be able to switch any input fiber with any output fiber to form new connection paths, which requires correct positioning of the mirrors in the new desired connection path. In the prior art, one method for determining whether the mirrors in a connection path are properly positioned is to employ a set of sensors (e.g., strain gages) for each mirror, whereby the position of the mirrors are monitored relative to a frame of reference, and mirrors are positioned based on sensor feedback information. This technique is undesirable, as it requires extra components (e.g., the strain gages and associated signal processing circuitry) that must also be calibrated and may fail, and increases the size and complexity of the optical switching device. Accordingly, it is desired to provide a scheme for positioning the mirrors within an optical switching device such that misconnected paths are avoided without requiring additional components, and selected input fibers may be readily connected to new output fibers to form new signal paths.
A method of positioning movable mirrors so as to maintain signal path integrity in an optical switch is described. The method is suitable for use in optical switching devices that enable selective connection of optical signals received on a plurality of input fibers to respective output fibers, wherein the optical switching device includes a first array of mirrors substantially disposed in a first mirror plane and a second array of mirrors substantially disposed in a second mirror plane. In accord with the method, all mirrors are continuously maintained in signal paths, while setting up a single new path at a time. A mirror in the second mirror plane is moved into a correct position while controlling the position of other mirrors so as to prevent undesired light from being directed upon the mirror or toward an output fiber corresponding to the new signal path. A light signal is provided to an input fiber corresponding to the new signal path, and the light signal is directed toward a mirror in the first mirror plane. The mirror in the first mirror plane is moved to direct light toward the mirror in the second mirror plane. The new signal path is confirmed to be properly configured by observing a change in light intensity at the output fiber corresponding to the new signal path.
Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.